Replacing Radiators - column or convection, double, single, BTUs!?

delmonta

Hi, all my current radiators seem to be old connection ones, just a single panel on the front with some small fins on the back, no casing. Most of the TRVs are broken, and I thought maybe it was worth replacing the rads when getting new TRVs.

Its a victorian house so I'd ideally like to get some more traditional column radiators for downstairs at least. They are expensive, but look much nicer. I was wondering about the BTU calculators, do they tend to be quite accurate? If the BTU calculator says I need 4500BTU for example, then if I get a 5000BTU radiator, will it be enough or is it possible it will struggle or take a long time? I imagine having a higher BTU radiator is always better isn't it? It will just heat up more quickly but still turn off when it reaches temperature. Maybe I'm wrong?

Also, I'd rather not have the convection rads sticking out into the room too much , so was planning to go with the type 11 rads, but I could put in the type 22 ones with a front and back panel. The BTU is basically double, and twice what the calculator says I need for my room. Is this overkill? I'm a bit worried the type 11 ones will be just the same as the old ones I currently have, although they do appear to have slightly deeper fins

And finally, is it fine to replace a horizontal radiator with a vertical column one?

thanks

FreeBear

I found the online BTU calculators produce variable results. I'd suggest trying a few, and then pick the higher number to be on the safe side. Going for a larger rated radiator is always preferable to one that is too small in my opinion as long as the boiler has enough capacity. No good having 30KW of radiators if your boiler is only rated at 24KW. If the calculator says you need 4500BTU, and the nearest available is a 5000BTU, go for that one. With a TRV set up properly, once the room is up to temperature, the heat will be diverted to the other radiators.

In terms of radiator selection, traditional cast iron style column radiators are quite bulky... Regular flat panels don't stick out as much. A single panel, single row of fins is a type 11 - Fairly low profile in terms of how far from the wall they project. A double flat panel with a double row of fins (a type 22) sticks out a long way and may be quite intrusive, particularly in a small room. I favour a double panel, single row of fins (type 21) - sticks out a little more than a type 11, but is not as huge as a type 22.

BUFF

If you need for e.g. a 4500BTU output rad & you put install a 5000BTU rad you should be fine as you have overspec'd slightly (the room should heat up slightly faster but the TRV will still shut it off once required temp. achieved).
As for speed of response this can vary according to the material used (e.g. cast iron vs steel) & amount of water content.

A type 22 will be deeper than an 11 but the point is that by doing so you could use a narrower/shorter rad for the same/similar output thereby freeing up wall space or installing where a 11 of required output wouldn't fit but a 22 would.
A modern rad is likely to be slightly more efficient than an older generation of similar design. Also won't be potentially sludged up.
 If you can, when installing the new TRVs I would recommend using horizontal as they tend to work slightly better than vertical (sensor is slightly further from the hot rad). & make sure the system is balanced.

As for replacing a horizontal rad with a vertical you may have to adjust the pipes to suit plus especially in an older building that isn't as well sealed/insulated as modern depending upon it's exact width/height/location in the room & whether it's the only heat source in the room I could imagine that it may change the way that heat disseminates slightly compared to a wider horizontal rad..

vacheron

Also check the BTU capacity of your boiler to ensure that it can deliver the amount of heat that the radiators are attempting to dissipate.

You could uprate all your radiators, but if the total exceeds the output capacity of the boiler, then the house as a whole will not heat up any quicker than it currently does, (though some rooms may heat quicker than others unless your plumber properly re-balances the system which is a time consuming process which very few plumbers will do properly).  

nofoollikeold

1. The various heat loss calculators do, as mentioned above, produce different results.  Given that your house is Victorian I personally wouldn't rely on any of them.  The best method is the one published by CIBSE, but you have to buy the book, and I don't think there is an online version.
2. You really need to know the construction of the house and materials used.  Likely to be solid brick walls and single glazing with high ceilings.  Any insulation added? and if so, where and thickness.
3. Traditional column radiators are clearly much heavier than normal radiators, and often need feet to rest them on the floor.  I would say you cannot attach them to anything other than a brick / block wall, and certainly not to plasterboard with a gap behind.
4. As vacheron has said above, make sure your boiler can cope with the load.,
5. Also, if you have a sealed system, then the expansion vessel may not be big enough for larger radiators because of the increased volume of water in the system.  This particularly applies to column radiators.  
6. Don't forget to allow for pipework alterations.  Even if you keep the same width of radiator, any difference in depth of the pipe centres from the wall will require changes.  

delmonta

FreeBear said:

I found the online BTU calculators produce variable results. I'd suggest trying a few, and then pick the higher number to be on the safe side. Going for a larger rated radiator is always preferable to one that is too small in my opinion as long as the boiler has enough capacity. No good having 30KW of radiators if your boiler is only rated at 24KW. If the calculator says you need 4500BTU, and the nearest available is a 5000BTU, go for that one. With a TRV set up properly, once the room is up to temperature, the heat will be diverted to the other radiators.

In terms of radiator selection, traditional cast iron style column radiators are quite bulky... Regular flat panels don't stick out as much. A single panel, single row of fins is a type 11 - Fairly low profile in terms of how far from the wall they project. A double flat panel with a double row of fins (a type 22) sticks out a long way and may be quite intrusive, particularly in a small room. I favour a double panel, single row of fins (type 21) - sticks out a little more than a type 11, but is not as huge as a type 22.

Thanks, ok so going a little over what the calculators say is not a bad idea, but getting something rated double the BTU would not be a great idea, most likely because the boiler would not be capable. I will try and find out what my boilers limits are

I am looking at modern column radiators that replicate cast iron, so not as heavy and cheaper, such as this : https://www.bestheating.com/milano-windsor-horizontal-triple-column-anthracite-traditional-cast-iron-style-radiator-600mm-x-785mm-59380

Thats for the kitchen. For the bedrooms I was planning on the cheaper ones as you described. The type 22 does seem like its going to stick out too much, so maybe type 11 is the way to go

delmonta

BUFF said:

If you need for e.g. a 4500BTU output rad & you put install a 5000BTU rad you should be fine as you have overspec'd slightly (the room should heat up slightly faster but the TRV will still shut it off once required temp. achieved).
As for speed of response this can vary according to the material used (e.g. cast iron vs steel) & amount of water content.

A type 22 will be deeper than an 11 but the point is that by doing so you could use a narrower/shorter rad for the same/similar output thereby freeing up wall space or installing where a 11 of required output wouldn't fit but a 22 would.
A modern rad is likely to be slightly more efficient than an older generation of similar design. Also won't be potentially sludged up.
 If you can, when installing the new TRVs I would recommend using horizontal as they tend to work slightly better than vertical (sensor is slightly further from the hot rad). & make sure the system is balanced.

As for replacing a horizontal rad with a vertical you may have to adjust the pipes to suit plus especially in an older building that isn't as well sealed/insulated as modern depending upon it's exact width/height/location in the room & whether it's the only heat source in the room I could imagine that it may change the way that heat disseminates slightly compared to a wider horizontal rad..

Thanks, as for replacing the horizontal one, there will be some pipework needed to get it where I want it, but shouldn't be too hard. The current rad is behind the sofa, which doesnt make sense. So I'm hoping this will let us feel the heat more quickly in the air

delmonta

nofoollikeold said:

1. The various heat loss calculators do, as mentioned above, produce different results.  Given that your house is Victorian I personally wouldn't rely on any of them.  The best method is the one published by CIBSE, but you have to buy the book, and I don't think there is an online version.
2. You really need to know the construction of the house and materials used.  Likely to be solid brick walls and single glazing with high ceilings.  Any insulation added? and if so, where and thickness.
3. Traditional column radiators are clearly much heavier than normal radiators, and often need feet to rest them on the floor.  I would say you cannot attach them to anything other than a brick / block wall, and certainly not to plasterboard with a gap behind.
4. As vacheron has said above, make sure your boiler can cope with the load.,
5. Also, if you have a sealed system, then the expansion vessel may not be big enough for larger radiators because of the increased volume of water in the system.  This particularly applies to column radiators.  
6. Don't forget to allow for pipework alterations.  Even if you keep the same width of radiator, any difference in depth of the pipe centres from the wall will require changes.  

The house is solid walls, but the reason I'm doing this is because I'm having the front of the house internally insulated and the rear externally insulated. So after that it should be quite efficient, meaning the rads won't have to work so hard. 

The column rads I'm looking at are steel I think, like a modern mimic of cast iron ones. I've put a link above

Thanks

FreeBear

Type 21 radiators are a good compromise if you don't want them sticking out too far..

As you are having the walls insulated, I'd suggest hanging the radiators on an internal wall - Traditionally, radiators are stuck under a window to combat the heat loss through the glass and the resulting cold draught. With good levels of insulation and decent double/triple glazed windows, there shouldn't be any cold draughts. Also, hanging the radiators on an insulated wall means some thought has to be given to providing adequate support. A radiator full of water is a heavy thing and needs to be bolted securely to a wall.

delmonta

FreeBear said:

Type 21 radiators are a good compromise if you don't want them sticking out too far..

As you are having the walls insulated, I'd suggest hanging the radiators on an internal wall - Traditionally, radiators are stuck under a window to combat the heat loss through the glass and the resulting cold draught. With good levels of insulation and decent double/triple glazed windows, there shouldn't be any cold draughts. Also, hanging the radiators on an insulated wall means some thought has to be given to providing adequate support. A radiator full of water is a heavy thing and needs to be bolted securely to a wall.

thanks, the type 21 radiators of the same size (meaning I won't have to move pipes) are about double the BTU rating that I supposedly need, and twice the price. So I'm not sure this is necessary considering the room will also be insulated soon. 

As for hanging on an internal wall, it would mean taking up floorboards and moving all the pipework, seems like a lot more work. You are right they are currently under the windows, but to be honest in both rooms it sort of makes sense and looks quite neat being under the windows. I cant see much of a better place without moving them to the other side of the room! which would be a hassle

Thats why I wanted to work this out now, so I can get the people doing the insulation to put some stud work in exactly where I need to fix the rads

Leethos

Hi, the one point which has been raised above that needs consideration is that of the expansion vessel. A column radiator even the modern steel type will have a greater water content than a steel panel radiator of the same size. You need to factor in the volume of water in the system and ensure that the vessel in the boiler has spare capacity to take up the additional expansion required if you opt for a number of column radiators.